#define _CRT_SECURE_NO_WARNINGS 1

class Solution {
public:
    int takeAttendance(vector<int>& nums) {
        int left = 0, right = nums.size() - 1;
        while (left < right)
        {
            int mid = left + (right - left) / 2;
            if (nums[mid] == mid) left = mid + 1;
            else right = mid;
        }
        if (nums[left] == left) return nums.size();
        else return left;
    }
};


class Solution {
public:
    int missingNumber(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        int left = 0, right = nums.size() - 1;
        while (left < right)
        {
            int mid = left + (right - left) / 2;
            if (nums[mid] == mid) left = mid + 1;
            else right = mid;
        }
        if (nums[left] == left) return nums.size();
        else return left;
    }
};  